title: The viscosity of dilute poly(N-isopropylacrylamide) dispersions.
abstract: The viscosity of dilute aqueous dispersions of poly(N-isopropylacrylamide) microgel particles is measured by capillary viscometry. The viscosity increases with particle mass fraction and on reducing temperature, particularly below the volume phase transition temperature (VPTT) of 32 °C. Converting the particle loading to volume fraction via the change in hydrodynamic size, the slope of the viscosity-volume fraction graph exhibits an increasing value beyond that for the equivalent effective hard-sphere size as the particles swell. This increase is due to the porosity of the particles. Two microgel samples of different collapsed size (124 and 59 nm at 50 °C) are investigated and the deviation from hard-sphere behavior is greater for the smaller particles.
authors.affiliation: BP Institute for Multiphase Flow, University of Cambridge, Madingley Rise, Cambridge CB3 0EZ, United Kingdom.
authors.forename: Anya J
authors.initials: AJ
authors.lastname: Howe
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Howe
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Routh